1. Technical Field
The present invention relates to a constant voltage generating circuit and a constant voltage generating method, and more particularly, to a constant voltage generating circuit which generates a constant voltage with respect to a variable power supply voltage without using a regulator, and a constant voltage generating method.
2. Description of the Related Art
One of the items determining the design of electronic circuit systems is a power supply voltage level. Even in the same application, an optimized power supply voltage level may differ for each system. Accordingly, there are many cases in which an integrated circuit used in the system is required to be designed based on a variable power supply voltage. When a power supply voltage varies, a voltage and a current of each node of the circuit may vary. These variations may cause many problems in linearity of the circuit, noise, and management of power consumption.
To generate a power supply voltage of a constant level with respect to a variable power, a regulator may be frequently used. However, in order to output a constant voltage using a regulator, additional circuits such as a Band Gap Reference (BGR), a Low Drop Output (LDO), and the like other than the regulator may be required. A regulator output voltage with superior performance is obtained when a regulator system is constituted using the additional circuit; however, the volume of the circuit and power consumption may be increased.
FIG. 6 shows a regulator system having a general structure in the related art. When a width of a variable power is large, or an input power supply voltage is significantly larger than a final regulator output, a primary regulator 1 may be used as shown in FIG. 6. A variation ratio of an output voltage of the primary regulator 1 is at least 10% or larger, and therefore, an accurate output voltage may be obtained through an LDO that is a secondary regulator 2. Accuracy of the voltage that is output by the LDO 2 depends on the accuracy of a BGR 3. This is because the LDO 2 multiplies a BGR voltage received as an input to thereby output an output voltage. Here, the primary regulator 1, the BGR 3, and the secondary regulator 2 which are used to obtain a constant output voltage in FIG. 6 have superior performance; however, each block of the primary regulator 1, the BGR 3, and the secondary regulator 2 is heavy, so that problems in power consumption and a size may be generated in a circuit requiring low power and miniaturization.